With the continued scaling down of the magnetic head used in hard drives, improved magnetic signal-to-noise ratio in the magnetic head and media is needed for a new generation of hard drives. To improve performance, ultra thin (e.g., less than about 3 nm) carbon overcoat (COC) has been used in the fabrication of new generations of head and media. The carbon overcoat is fabricated to achieve the desired chemical state in order to ensure the mechanical and/or thermal properties needed for the prescribed performance specifications of the head and media. This can be partially achieved by using unpatterned full (or thick) film monitor coupons, that are used to monitor a workpiece wafer. The coupon is a separate wafer such as a silicon wafer that is processed in substantially the same way as the workpiece wafer.
However, the generally known characterization methods of thick films becomes unreliable when the thickness of the carbon overcoat is less than about 3 nm. It is because thin carbon overcoat is intrinsically and chemically different from thick films. Therefore, conventional characterization methods applied to thick films become unreliable and less sensitive in measuring thickness, composition, and chemical bonding when the film thickness drops below about 3 nm. Additionally, the carbon overcoat at different locations of a head has different properties depending on the areas, such as substrate, shield, where the carbon overcoat is grown on. Therefore, a reliable technique is needed to fully characterize the carbon overcoat used in head and media development and manufacturing processes.
Various methods have been used to characterize the chemical bonding information (sp3/sp2 ratio) of carbon overcoat films, such as Raman spectroscopy, solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS) in transmission electron microscopy (TEM). While Raman, NMR, and XPS are useful techniques, the carbon overcoat generally needs to have a thickness more than about 3 nm to carry out the measurement with a reasonable signal-to-noise ratio. While EELS can work on thinner films down to sub-nanometer in thickness, there is no known direct way to detect a sp3/sp2 ratio of a carbon overcoat (COC) using EELS.